ST. PETERSBURG, Fla. -- Even after two straight days of facing Koji Uehara, the Tampa Bay hitters can't quite figure out what he does that makes him so effective.

ST. PETERSBURG, Fla. -- Even after two straight days of facing Koji Uehara, the Tampa Bay hitters can't quite figure out what he does that makes him so effective.

The Rays aren't alone, of course. Uehara has mowed down a franchise-record 34 straight hitters to dig in against him -- hitters from San Francisco, Los Angeles, Baltimore, Chicago, Detroit and New York. He's struck out 16 of those 34 hitters, and he's averaged fewer than 12 pitches per inning.

"I can't put my finger on it," said Tampa Bay rookie Wil Myers, who has popped out and struck out against Uehara. "He's obviously got a good splitter. But his fastball is really good, too -- and it's straight. I don't know what it is. I can't put my finger on it."

Here's what the Rays have been able to ascertain about what makes Uehara so effective: He throws a fastball with "good carry," as Ben Zobrist described it. Most pitchers throw with a downward angle that's easier for a hitter to track, giving them a chance to see if it's going to come in at the knees or if it's going to come in below the knees. Because of the way Uehara throws his fastball, it often can look like it's coming in low but still winds up crossing the plate at the knees for a strike.

"I don't know if it's a rotational thing, but it looks like a four-seam and it's just going 89, but instead of going 89 like this, it goes 89 like this," said Zobrist, demonstrating with his hands what amounts to an upward kick at the end of the trajectory of the pitch. "You think you're right on it, and you foul it back. You're like, 'How did I miss that? I saw it great. It was right there.' But you foul it right back because it has that little bit of extra carry."

Uehara isn't the only pitcher who throws that type of "extra carry" fastball. Several different Tampa Bay hitters said they've seen Rays starter Matt Moore and reliever Joel Peralta do the same thing.

According to BrooksBaseball.net data, Moore throws the fastball with the highest rate of rotation in the major leagues -- more than 57 rotations per second. Uehara's 36.2 rotations per second rank him in the top 10 percent of major-league pitchers. At the other end of the scale are pitchers who rely more on sink like John Lackey (18.5 rotations per second) or Felix Hernandez (15 rotations per second).

"Even though it might say 92 on the board, it's acting a lot more like 95," Zobrist said, gesturing toward Moore. "If it's 95, then it's going to be more like 98. If you're swinging on the plane of the ball or you're trying to come up to get it, to hit a line drive, you're going to be a tick late -- unless you plan on getting on top of the ball."

But hitters can't swing to get on top of the ball against Uehara, not with the splitfingered fastball he throws. That's a recipe for helplessness for hitters.

"The splitfinger looks the exact same coming out of his hand," Zobrist said. "If it comes out on the same plane as the fastball, it's going to drop out of the zone and you swing at it anyways."

The other thing Uehara does so well is throw off the timing of the hitter with the pace of his delivery. He throws the ball with arm speed hitters usually associate with a mid- or upper-90s fastball, but the pitch comes in at 89 or 90 miles per hour. In that way, because it leads to deception, he's more effective at 89-90 than he would be at 94-95.

"He's one of those guys, when you're in the batter's box, that has the delivery, the tempo and everything else that really feels like the ball is coming out really quick," said Kelly Johnson, who struck out against Uehara on Wednesday night. "The arm action, the way he comes at you, is very quick in your mind, but then the ball isn't quite as at that same velocity."